The present invention is directed to an optical device for monitoring critical speeds of a rotating member.
With rotating members, such as rotors, which are rotating at high speeds for example in turbines, centrifuges, machine shafts, problems will often occur. These problems are that a specific speed dare not be exceeded or that the appertaining device dare not be operated in a range of a critical speed.
Previously known methods of tachometry or, respectively, speed monitoring either make use of purely mechanical or made use of electromagnetic means. The measuring methods by means of purely mechanical means has many disadvantages such as relatively high wear and, thus, a short service life. In addition, the mechanical measuring method has the disadvantage, which due to the necessary mechanical coupling to the rotor, which is to be monitored, requires that the tachometer be installed at a location of the device to be monitored. Electromagnetic tachometry methods have the advantage with respect to pure mechanical tachometry methods because electromagnetic methods may have a special arrangement and they need not be bound to the location or site of the machine whose rotating member is being monitored. However, in certain cases, it might be disadvantageous that an electrical connection exist between the device to be monitored and the measuring and/or displaying means.